1. Field of the Invention
The invention relates generally to the art of plastic bag making machines. More specifically, the present invention relates to a bag machine which employs a rotary sealing drum. Still more specifically, the present invention relates to a bag machine in which the sealing drum is adjustable in size to produce different bags of different sizes and in which the drum mechanism is designed to compensate automatically for slight corrections in the spacing of heat seals while the bag making machine is operating.
2. Description of Related Areas of Art
Many different types of plastic bag making machines are known to the art for producing plastic bags for industrial and individual consumers for many different applications (e.g. small sandwich bags and trash bags). While the present invention has a wide range of applications for the production of such products, the related art will be explained by reference to one particular class of bags, i.e., polyethylene trash bags or, garbage bags and wastebasket liners of the type usually sold in boxes of folded bags or rolls of bags.
Further discussion of the history and operation of these machines can be found in U.S. Pat. No. 4,642,084 entitled "Plastic Bag Making Machine", issued to the present inventor on February 10, 1987 and assigned to Custom Machinery Design, Inc. ("Gietman U.S. Pat. No. '084"). That patent discloses a bag machine which includes a rotary drum constructed of a plurality of slats and which includes a gear mechanism adapted for infinite variation of the drum diameter between a first smaller diameter and a second larger diameter. A sealing blanket is provided for the drum and is automatically adjusted for different drum diameters to provide proper tension on the film as it passes around the expandable drum.
In that configuration, manual rotation of a hex nut assembly while the machine is stopped increases or decreases the drum's diameter through a series of appropriately mounted mitre gears and ring gears. Once this adjustment is made, the machine begins operation. Readjustment of the drum diameter can only be accomplished by stopping the machine to adjust the hex nut assembly.
Additionally, very small errors in drum diameter size can lead to acute problems, particularly when the film passing through the machine has preprinted material thereon which has to appear at the same relative position on each bag. An error of a fraction of an inch leads to serious problems when the bag width is only several inches across and the speed of the film moving through the machine is 500-900 bags per minute. By the time the error is detected, a considerable amount of film is wasted. Furthermore, the mistake is irreparable since the heat seals and perforations can not be "corrected".
A bag making machine which overcomes these shortcomings and those noted in the Gietman U.S. Pat. No. '084 would represent a considerable advancement in the art.